of trust, authority, or supervision in relation to the victim, and the victim is at least 13 years of age but under 18 years of age.

(b) Sentence. (1) Criminal sexual assault is a Class 1 felony,

except that:

(A) A person who is convicted of the offense of

criminal sexual assault as defined in paragraph (a)(1) or (a)(2) after having previously been convicted of the offense of criminal sexual assault or the offense of exploitation of a child, or who is convicted of the offense of criminal sexual assault as defined in paragraph (a)(1) or (a)(2) after having previously been convicted under the laws of this State or any other state of an offense that is substantially equivalent to the offense of criminal sexual assault or to the offense of exploitation of a child, commits a Class X felony for which the person shall be sentenced to a term of imprisonment of not less than 30 years and not more than 60 years, except that if the person is under the age of 18 years at the time of the offense, he or she shall be sentenced under Section 5-4.5-105 of the Unified Code of Corrections. The commission of the second or subsequent offense is required to have been after the initial conviction for this paragraph (A) to apply.

(B) A person who has attained the age of 18 years

at the time of the commission of the offense and who is convicted of the offense of criminal sexual assault as defined in paragraph (a)(1) or (a)(2) after having previously been convicted of the offense of aggravated criminal sexual assault or the offense of predatory criminal sexual assault of a child, or who is convicted of the offense of criminal sexual assault as defined in paragraph (a)(1) or (a)(2) after having previously been convicted under the laws of this State or any other state of an offense that is substantially equivalent to the offense of aggravated criminal sexual assault or the offense of predatory criminal sexual assault of a child shall be sentenced to a term of natural life imprisonment. The commission of the second or subsequent offense is required to have been after the initial conviction for this paragraph (B) to apply. An offender under the age of 18 years at the time of the commission of the offense covered by this subparagraph (B) shall be sentenced under Section 5-4.5-105 of the Unified Code of Corrections.

(C) A second or subsequent conviction for a

violation of paragraph (a)(3) or (a)(4) or under any similar statute of this State or any other state for any offense involving criminal sexual assault that is substantially equivalent to or more serious than the sexual assault prohibited under paragraph (a)(3) or (a)(4) is a Class X felony.